Breathing Oxygen is used onboard cruise vessels for medical emergency situations where a passenger requires assistance with breathing.
Breathing Oxygen cylinders are fitted with Yoke-type / PISS valves, which are familiar to the majority of the Cruise vessel's staff. The 40 liter cylinder is also used for ships transporting dangerous goods according to the IMDG which have the requirement to have this type of oxygen onboard for emergencies.
Be aware: The filling pressure is lower than the mentioned 200 bar in some locations due to local rules and regulations that limit the filling pressure.